Ultraviolet vacuum ultraviolet optical functions for SrTiO3 and NdGaO3 crystals determined by spectroscopic ellipsometry

Abstract

Complex dielectric functions ε(E) = ε1(E) + ε2(E) were experimentally evaluated within the spectral range E = 2–25 eV and E = 2–20 eV for SrTiO3 and NdGaO3 single crystals, respectively, using synchrotron-based spectroscopic ellipsometry measurements. The ellipsometric spectra were evaluated within a framework of optical layer model taking into account sample surface roughness and anisotropy of NdGaO3. The parameters of Herzinger-Johs oscillator model were fitted to reproduce sufficiently all features of the optical spectra within the spectral range 2–10 eV. Only slight differences were revealed for spectra polarized along b and c crystallographic axes of the NdGaO3, which can confirm weak optical anisotropy.

Temperature-dependent dielectric function of bulkSrTiO3: Urbach tail, band edges, and excitonic effects

“…Note that measurements outside the cryostat in ambient conditions result in a thickness of 2.1 nm. These values are consistent with previous ellipsometric studies on STO and also with the fact that the adsorbed overlayers decrease in ultrahigh vacuum conditions due to desorption 40,47 .…”

“…While converting previously reported dielectric function data from Cardona and others 30,36 to refractive index and extinction coefficient, apparently the data was redshifted by ∼200 meV 59 . This mistake was then repeatedly reported by various later authors along with their new results, each explicitly highlighting these discrepancies 5,40,42,47 . We find that the original data by Cardona in fact agree quite well with most subsequent reports.…”

“…Optical spectroscopy techniques and particularly spectroscopic ellipsometry can be used to determine the dielectric function, which provides valuable information about the electronic structure of the material. Not surprisingly, there have been numerous experimental studies on STO in the past with the aim of elucidating the electronic structure employing various types of optical spectroscopies [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] . Simultaneously, many theoretical studies have been performed on STO using different approaches [49][50][51][52][53][54] .…”

Optical properties of epitaxial Na0.5Bi0.5TiO3 lead-free piezoelectric thin films: Ellipsometric and theoretical studies

“…The spectra were evaluated by transfer matrix calculations within a layered optical model being STO substrate/NBT film/surface imperfection. The optical constants for the STO substrate were taken from our previous study [9]. The roughness of the surface was approximated by effective medium theory (effective medium approximation EMA) according to Bruggeman [10], assuming 50% of voids in the matrix of NBT.…”

Оптические переходы с остовных d-уровней арсенида галлия

“…В данной области энергий точность таких измерений составляет ∼ 0.1−0.01 eV. Полученные экспериментальные результаты для полупроводников [12][13][14][15][16][17][18][19] показывают, что, вследствие перечисленных выше особенностей, спектры оптических функций в области переходов с остовных уровней содержат до восьми-девяти максимумов и ступенек.…”